I'm behind a firewall and all of a sudden, I'm unable to access Stack Exchange sites. I checked with the IT team and here is what they had to say:

We have analyzed the site: stackoverflow.com. There is no blockage in the proxy level. Analysis revealed that browsing traffic was reaching the stackoverflow.com domain but there was no reverse traffic coming back from the domain. We suspect that the public IP addresses of proxy servers might be blocked in their premises which has to be taken up with the stackoverflow IT team for releasing the same.